1. Field of the Invention
This invention relates to computer displays and methods for their manufacture, and more particularly to structures that enhance a display's stiffness.
2. Description of the Related Art
Flat panel displays are typically used as display devices in portable computer systems, and are increasingly being used as displays for conventional computer systems, for example desktop computer systems and workstations. Because flat panel display devices are relatively thin, a display assembly is also relatively thin, and therefore it is often convenient to attach the display assembly to a computer system using a clutch system or hinges. Such attachment is very common in portable computer systems.
The display clutch in a portable computer is the interface between the display assembly and the base of the computer. The clutch allows the display to pivot open and closed, and its resistance to torque allows the weight of the display assembly to be supported, thereby opposing gravity. Portable computers typically have a clamshell design where the base of the computer forms one part, and the display assembly forms the second part. The display assembly usually includes a rear shell or housing, a front cover or bezel with an opening for viewing the display device, a display device sandwiched in-between, and associated hardware (e.g. hinges, clutch supports, shafts and mounting brackets). The display assembly, and indeed the entire case of the portable computer, is usually constructed from plastic. Additionally, the most common way to open and close the portable computer is by grasping the display assembly at a point farthest from the hinge. The opening and closing forces imposed by a user are transmitted through the display assembly to the display clutch, leading to flexing of the display assembly as the user works to overcome the resistance of the clutch.
Consequently, flexing of display assemblies in computer systems that use flat panel displays, particularly portable computer systems, is quite often a source of design frustration and can result in a perception of poor quality on the part of users. Moreover, unwanted flexing in a display assembly can lead to structural weakness or failure of the display assembly and one or more of its components.
FIG. 1 illustrates a prior art design for flat panel displays used in portable computers. Display assembly 100 includes display shell 105 which provides a rear support and housing for display device 110. Display device 110 can be any type of flat panel display device including, for example, liquid crystal displays, plasma displays, and field emission displays. Display device 110 is secured to display shell 105 by way of frame 115. Frame 115 extends around the periphery of display device 110, including the sides and portions along the top surface of the display device near its edges. Frame 115 can be a separate frame, or an integral portion of display device 110, and typically includes through-holes or lugs through which fasteners can secure the display device to the shell. Mounting bracket 120 attaches and secures the display shafts 130 to the display shell 105. Display clutches 140 are coupled to the base (not shown) of the portable computer and receive shafts 130. Display device 110 is itself relatively stiff, adding to the stiffness of the display assembly, but only to the point of its lowest attachment to display shell 105. Similarly, mounting bracket 120 also adds stiffness to the display assembly, but only to the extent that it is attached to display shell 105.
FIG. 2 is a partial cross-sectional view of display assembly 100. Mounting bracket 120 is attached to display shell 105 (possibly through shafts 130) using fastener 125, thereby sandwiching display shaft 130 between itself and the display shell. Reference number 200 indicates a weak region of the display assembly located between mounting bracket 120 and display device 110. As mentioned above, display device 110 and mounting bracket 120 provide stiffness to the display assembly to the extent that 110 and 120 are themselves stiff, and limited by their attachment to display shell 105. In operation, a force applied to display assembly 100 results in a torque load transferred at weak region 200. So for example, when a force is applied to the assembly in the closing direction, display assembly 100 flexes at weak region 200, causing mounting bracket 120 and display device 110 to be deflected toward each other. When a force is applied to the assembly in the opening direction, display assembly 100 flexes at weak region 200, causing mounting bracket 120 and display device 110 to be deflected away each other. Both types of flexing, but particularly the latter type, give users the perception of poor quality, and the unwanted flexing in the display assembly can lead to structural weakness and/or failure of the display assembly and its components.
Prior methods of preventing undesirable flexing in display assemblies have proven to be unsatisfactory. Stiffening agents added to the plastic of the display shell offer minimal incremental stiffness to the assembly and add the risk of brittleness and cracking. A bezel or front display shell portion adds slightly to the stiffness of a display assembly, but a bezel or front display shell cannot be structurally tied to a display device adequately, and therefore the added stiffness is not significant. Increasing the thickness of the display shell and/or adding ribs to the display shell in the weak region can eliminate some of the flexing, but these solutions do not sufficiently eliminate flexing and may add unwanted thickness to the display assembly. Some designs have extended the mounting bracket up and behind the display device thus adding another layer of much stiffer material to the weak region. However, this solution includes significant weight and thickness penalties.
Accordingly, it is desirable to have a simple, thin, light component that can be included in a display assembly and minimizes flexing of the display assembly.